As I read it, the TalkBoard rule seems to deal with people who simply wish to change their handle because they'd prefer a different one. When someone comes along afterward, however, and signs up with a handle that's very similar to their own and could easily result in confusion and PMs being sent to the wrong person, it seems that's a different matter and one that's briefly addressed in the TalkBoard-approved Guidelines and Rules:

Before you can post, you must register with FlyerTalk and establish a username. Your username is a unique and consistent identifier, and serves as your identity on the forums. If you have concerns that a new username is very close to your own, please contact a moderator.

It seems to me there's some contradiction here and also that a long-time member should not be penalized with having to change names and start over from scratch when a newcomer choses a very similar variation on their handle. I don't know who should address this, but the TB policy and the TOS don't quite seem consistent on this one nor does the TB policy address handles that are so similar as to be confusing (scavenger vs. scavanger and singlemalt vs. single malt).